A significant decrease in immune responsiveness occurs with advancing age. The clinical consequences of immunosenescence include an increased susceptibility to and/or severity of infectious disease. Several intervention strategies have been proposed to restore immune function. One of the least well-studied approaches to improve immune response is physical exercise. The long term research objectives of our research group are to elucidate the mechanisms underlying the adaptations induced by moderate exercise that enhance immune responsiveness to infectious disease in aged populations. In this application, one goal is to determine the mechanistic adaptations induced by exercise that affect the initial pathways involved in recognition of viral infection that result in enhanced IFNalpha production. A second goal is to identify which of the pathways that can be triggered by IFNalpha lead to improved viral clearance and reduced immunopathology. The specific aims are: 1) Identify the mechanism(s) by which exercise training of aged animals increases IFNalpha production after influenza virus challenge, 2) Determine the extent to which the exercise-induced increase in IFNalpha regulates responses of dendritic cells and CD8+cells, 3) Identify the pathways involved in the response to IFNalpha that are altered by exercise, and 4) Further define the impact of exercise by determining the balance between pro-inflammatory / anti-inflammatory cytokines within the lungs and the subsequent effect on immunopathologically-mediated tissue damage, identify the cells producing these cytokines, and establish the role of IFNalpha as a mediator of these effects. A mouse model of influenza viral infection will be used. Aged BALB/c mice will be assigned to a moderate exercise group for 10 weeks or a non-exercise group. After exercise training, some experiments will involve an in vivo viral challenge to examine immune responses that occur in the intact animals, whereas other experiments will involve the collection of cells from mice after exercise training, and exposure to viral challenge in vitro. Different techniques will be used to identify the type of cells responding to challenge as well as the multiple pathways involved. Upon completion of these studies, we expect to indentify the exercise-induced adaptations involved in cellular defense against viral infection that subsequently shape the evolving immune response resulting in improved viral clearance and reduced immunopathology.